FIG. 1 is a cross-sectional view of a prior art MEMS piezoresistive pressure sensor module 100. It provides excellent pressure measurements for a wide range of fluids across a wide range of low pressures.
The pressure sensor module comprises essentially two dies, one is a MEMS pressure sensing element 104 and the other is an application specific integrated circuit (ASIC) identified by reference numeral 106. A vacuum cavity 103 is formed between a diaphragm 105 and a substrate 107 in the pressure sensing element 104. When pressure is applied on the diaphragm 105, the diaphragm 105 deflects and creates stresses on a Wheatstone bridge (not shown) on the diaphragm and converts the diaphragm deflection into a measurable voltage change. The two dies 104 and 106 are mounted to a housing substrate 112 using an adhesive 114. Small-diameter bond wires 102 extend and connect between the MEMS pressure sensing element 104 and the ASIC 106. The bond wires 102 also extend and connect between the ASIC 106 and a lead frame 110.
The wires 102 add cost and are of course susceptible to failure. Eliminating wires that extend between the MEMS pressure sensing element 104 and the ASIC 106 and between the ASIC 106 and the lead frame 110 would reduce cost and improve the reliability of the MEMS pressure sensing element and MEMS pressure sensors.
A viscous gel 116 inside a pocket 101 protects the pressure sensing element 104, the ASIC 106, and the bond wires 102 from pressurized media, the pressure of which is to be measured. The gel 116 needs to be soft enough in order to transmit pressure. The gel 116 on the top of the diaphragm 105, however, can cause a power-on voltage shift of the signals output from the device if high charges are stored in the gel. The gel 116 can also affect sensing accuracy in a severe vibration environment because of its mass. The gel 116 is expensive especially in a large pocket with two separated dies or chips 104 and 106. Reducing the pocket size, eliminating the gel and bond wires, or at least reducing gel quantity, or replacing expensive gel by less expensive gel for lower cost and better performance, would be an improvement over the prior art.